For a large number of years, the speed of a flowing fluid has been measured by transmitting from ultrasonic transducers the ultrasonic waves in the fluid in the direction of flow of said fluid and in an opposite direction and by measuring the respective propagation of the waves emitted in both directions.
On the basis of the measurement of the speed of the fluid, it is easy to determine its flow and the volume of fluid which has flowed at the end of a given time. The ultrasonic fluid counters, when installed on site, can be placed next to a pressure regulator.
Pressure regulators are able to reduce the pressure of a gas of several bars to about 20 mbars upstream of ultrasonic gas counters.
Now, the fall of pressure in the regulator is a source of considerable noise and it has been observed that this fall of pressure may provoke parasitic ultrasonic waves having a high pressure amplitude and whose frequency or frequencies correspond to those of the ultrasonic transducers of the counter.
These parasitic ultrasonic waves are transmitted through the flow of the fluid as far as the ultrasonic transducers. This results in having significant measuring errors which are totally unacceptable.
One logical solution would consist of increasing the amplitude of the ultrasonic waves emitted by the transducers, provided the level of the noise generated by the regulator is not too high.
However, the increase of amplitude is technologically limited.
Another solution would consist of increasing the transmission frequency of the ultrasonic transducers, but this would result in increasing the energy consumption of the counter, which constitutes a drawback when operating on batteries.
In addition, the transmission frequency of the transducers can only be increased within certain limits, beyond which the transducers need to be replaced by higher frequency transducers. However, these transducers represent a change of technology with respect to the former transducers which sometimes risks questioning the characteristics of the ultrasonic measuring path and the electronics associated with said counter.